Within the hobby I think different folks have different definitions of what they think constitutes a variation. For my own purposes, I define a variation as a card that differs from it's counterparts because of some intentional change the manufacturer made to the card itself, or in the printing process involving the card.
Many cards contain unintentional print defects, some recurring, that cause the card to differ in some regards to it's counterparts . I personally refer to these as variants.
I would be the first to admit that in some cases it is impossible to determine after the fact if some recurring print defects just accidentally occurred on some print runs, or were discovered and intentionally changed.
I would also admit that no matter what definition of variation is adopted, there will be gray areas
Finally, no matter what definition anyone adopts, what really matters is hobby recognition via a catalog such as SCD or Becketts, or the Registry. Only then does a variant card become a must have for master set or player collectors, which in turn gives the card a premium value.
And, trying to predict what variants might some day make into master set lists can be a crap shoot, as exemplified by PSA adding the 61 Ron Fairly, with an errant green smudge of varying degrees in the baseball on the card back, to it's 61 master set list.
Persistence and or customer volume and status my be factors in what gets officially recognized these days as a "new" variation.
Either way, I find variants like those under discussion here fascinating, and I like to at least get examples of such differences for all my sets, and label them with notes in those sets. I had not noticed the back differences in the stock before, but the backs do differ some between yellowish and orangish as well. I was aware of the line issues that pop up in this set and the 68s and 69s, and have examples with each set
The internet, particularly ebay, and grading services have caused much closer scrutiny of cards, front and back in recent years. I tend to think that if you look long enough you might find some print variant of virtually any card
